Kidney transplantation offers a significant improvement in life expectancy and quality of life for patients with end stage renal disease. Unfortunately, graft losses due to allograft dysfunction or other uncertain etiologies have greatly hampered the therapeutic potential of kidney transplantation. Among various types of graft losses, subclinical acute rejection (subAR or SCAR) is histologically defined as acute rejection characterized by tubule-interstitial mononuclear infiltration identified from a biopsy specimen, but without concurrent functional deterioration (variably defined as a serum creatinine not exceeding 10%, 20% or 25% of baseline values).
A critically important challenge for the future of molecular diagnostics in transplantation based on peripheral blood profiling is to predict a state of adequate immunosuppression with immune mediated kidney injury before there is a change in the serum creatinine. This is the challenge of identifying subclinical acute rejection, which at this time is only occasionally and accidentally picked up by protocol biopsies done at arbitrary time points.
The terms subAR and SCAR are used interchangeably herein to refer to subclinical acute rejection. SubAR (or SCAR) is distinct from clinical acute rejection, which is characterized by acute functional renal impairment. The differences between subAR or SCAR and acute rejection (which may appear histologically indistinguishable on a limited sample) can be explained by real quantitative differences of renal cortex affected, qualitative differences (such as increased perforin, granzyme, c-Bet expression or macrophage markers), or by an increased ability of the allograft to withstand immune injury (‘accommodation’). SubAR or SCAR is often diagnosed only on biopsies taken as per protocol at a fixed time after transplantation, rather than driven by clinical indication. Its diagnosis cannot rely on traditional kidney function measurements like serum creatinine and glomerular filtration rates. Predicting graft outcomes strictly based on the kidney biopsy is difficult and this invasive procedure has significant costs and risks for patients. Organ biopsy results can also be inaccurate, particularly if the area biopsied is not representative of the health of the organ as a whole (e.g., as a result of sampling error). There can be significant differences between individual observers when they read the same biopsies independently and these discrepancies are particularly an issue for complex histologies that can be challenging for clinicians. In addition, the early detection of rejection of a transplant organ may require serial monitoring by obtaining multiple biopsies, thereby multiplying the risks to the patients, as well as the associated costs.
Transplant rejection is a marker of ineffective immunosuppression and ultimately if it cannot be resolved, a failure of the chosen therapy. The fact that 50% of kidney transplant patients will lose their grafts by ten years post-transplant reveals the difficulty of maintaining adequate and effective long-term immunosuppression. Currently, there are no other effective and reliable blood-based or any other tests for subAR or SCAR diagnosis. Thus, there is a pressing medical need to identify minimally invasive biomarkers that are able to identify subAR or SCAR at a time that changes in therapy may alter outcomes. The present invention addresses this and other unfulfilled needs in the art.